The back gear on my SB 9 had 3 teeth missing on the small gear. I decided to attempt a repair.
I cleaned the part thoroughly, then heated it up and filled the area of the missing teeth with braze. Let it cool (slowly) and evened out the top of the blobby braze a bit.
I made a fixture to mount it in my milling machine, and set up a 16DP 14.5PA #5 gear cutter. I used an indexer to carefully rotate the gear 15 degrees at a time, to carve slots in the braze to make new teeth.
The technique seemed to work, but something's not right. When I mount the gear back in the lathe and turn it on, I get a noticable "clacking" noise when the newly cut gear teeth go by the gear driving the chuck (bull gear?). I can feel vibration through the back gear handle, and if I don't hold the handle, it will kick itself out.
Needless to say, I'm not going to put any kind of load on this thing until I get it sorted out!
It acts like the cuts between the teeth are not deep enough or wide enough, such that the teeth on the bull gear are not meshing clean, and trying to kick the back gear out. But I've mic'ed the width and height of the teeth, and the depth of the cuts, and they seem fine. If anything, there should be a little *more* clearance than the stock teeth.
When I look at the cutter and the original teeth under magnification, they're close, but not a perfect match. The cutter doesn't get quite to the bottom of the cuts between the original teeth, and the cutter appears to have just a touch tighter curvature than the teeth. That last might be wear.
So what else should I look at? Anybody got experience repairing these things? I could just go buy a used gear, but I feel like a machinist, even an amateur one, should be able to fix this thing
I cleaned the part thoroughly, then heated it up and filled the area of the missing teeth with braze. Let it cool (slowly) and evened out the top of the blobby braze a bit.
I made a fixture to mount it in my milling machine, and set up a 16DP 14.5PA #5 gear cutter. I used an indexer to carefully rotate the gear 15 degrees at a time, to carve slots in the braze to make new teeth.
The technique seemed to work, but something's not right. When I mount the gear back in the lathe and turn it on, I get a noticable "clacking" noise when the newly cut gear teeth go by the gear driving the chuck (bull gear?). I can feel vibration through the back gear handle, and if I don't hold the handle, it will kick itself out.
Needless to say, I'm not going to put any kind of load on this thing until I get it sorted out!
It acts like the cuts between the teeth are not deep enough or wide enough, such that the teeth on the bull gear are not meshing clean, and trying to kick the back gear out. But I've mic'ed the width and height of the teeth, and the depth of the cuts, and they seem fine. If anything, there should be a little *more* clearance than the stock teeth.
When I look at the cutter and the original teeth under magnification, they're close, but not a perfect match. The cutter doesn't get quite to the bottom of the cuts between the original teeth, and the cutter appears to have just a touch tighter curvature than the teeth. That last might be wear.
So what else should I look at? Anybody got experience repairing these things? I could just go buy a used gear, but I feel like a machinist, even an amateur one, should be able to fix this thing